Piezo-electric crystal apparatus



Jan, 143 1936. R, E. FRANKLIN PIEZO ELECTRIC CRYSTAL APPRTUS Filed April 8, 19:52

ATTORNEY NVENTOR Patented Jan. 14, 1936 UNITED 'S TATES PATENT OFFICE Ralph E. Franklin-Port Jefferson, N. Y., assignor to RadioCorporation of America, a corporation of Delaware Application April 8,

9 Claims.

This invention relates to .improvements in piezo-electric apparatus, and more particularly to the mounting of the piezo-electric element.

Heretofore, the Apiezo-electric element which functions as the frequency control device, was mounted inahousing usually of metal and insulating material, such a housing generally having two or moreelectrodeswhich connect to a vacuum tube circuit. It has been found that the frequency of oscillations of the piezo-electric element varies with the thickness of the air gap Vbetween the element and the electrodes. There` fore-in order to maintain a constant frequency with a crystal housing utilizing a Yfixed air gap, it yisnecessary to fixthe position of the piezoelectric elements within the iixed air gap for the reason that due to mechanical difficulties the faces of the piezo-electric elements and the electrodes are seldom exactly parallel. If the piezoelectric element were allowed to move about to any great .extent in the-fixed air gap, the frequency of oscillations would vary appreciably.

It is an object of this invention to improve the accuracy of the frequency oscillation control by Xing and maintaining the position of the piezo velectric element which isinterposed between the electrodes in several different positions within a certain area of the electrodes which are located in the crystal housing.

Another object of this invention is to be able to interchange various sizes of piezo-electric elements within -the crystal housing.

The advantages obtained in a crystal holder housing wherein there is provided a means of interchanging and retaining various sizes and shapes of crystals, is the ease of changing the frequency of a transmitter without resorting to circuit changes, also the substitution of other crystals of dilierent characteristics.

Other objects and advantages will appear in the following detailed description.

In the drawing like references refer to similar parts throughout the several views in which,

Fig. l is a vertical cross section of the crystal holder assembly;

Fig. 2 is a plan View of the crystal holder assembly with the upper electrode or electrodes removed;

Fig. 3 is a plan View of the crystal holder assembly;

Fig. 4 is a side elevation of the crystal retaining ringer members;

Fig. 5 is a plan view of the crystal retaining finger members;

1932, Serial No.'603,920

Fig. 6 is aside elevation of the crystal retaining eccentric members, and

Fig. "I is a plan View of the crystal retaining eccentric members.

This improved electric crystal housing is best shown in Figs. l and 2 of the drawing in which I is a housing of molded bakelite or any other suitable insulating material, 2 is the lower electrode, 3 is the piezo-electric crystal element, 4, 5 and 6 are the electrode spacers which are made of quartz, glass, or any other suitable insulating material. As these insulating spacers are of greater thickness than the piezo-electric crystal 3, they form a fixed air gap in which the crystal 3 is free to oscillate, as indicated at l. The upper electrode 8, which may be of any sim or shape, is secured to the housing I by a suitable spring 9 pressing upon an insulating housing cover II) provided to keep out dust, moisture, etc. rIhe complete assembly is retained within the housing I by means of the spring 5 which is slotted at its ends II and I2. Suitable screws i3 and I4 are provided to fasten the spring to the housing. While this retaining means is shown, any other suitable retaining means may be provided. The crystal 3 is secured in position by means of a plurality of adjustable metallic nger members I5, I6, I'I and I8 which are composed of brass or other suitable metal and are shown in detail by Figs. ll and 5. These metallic fingers are forced snugly in suitable apertures in the lower electrode 2 and are set to give the crystal 3 a small clearance of a few thousandths of van inch, which is necessary to allow the crystal to oscillate freely.

If the crystal 3 were clamped or retained without the clearance between the finger members and the crystal as mentioned above, the crystal would be damped to such an extent that the starting of oscillations would be retarded.

Referring now to the modifications of crystal retainers the eccentric type of metallic members are shown in det-ail by Figs. 6 and 7. The eccentric type of retaining members can be substituted for the finger retaining members l5, I6, I 'I and I8, although they are. not shown on the drawing as assembled in Figs. l and 2. In assembly they are forced snugly in suitable apertures in the lower electrode 2, and are adjusted to give the necessary clearance as mentioned above. The crystal spacers 4, 5 and t are loosely tted and held in proper position on the lower electrode 2 by means of suitable screws I9, 20 and 2l.

` Although this invention has been described and illustrated, it is apparent that other modifications in its construction may be varied in order to obtain the desired results, and yet retaining the fundamental principles of this device within the spirit and scope of the appended claims.

I claim:

1. A piezo-electric crystal housing including an insulating housing, a lower electrode, an upper electrode, both retained within said housing, insulating members between the lower and upper electrodes forming a xed air gap, a piezo-electric crystal interposed between said electrodes and adjustable elements located in the lower electrode to adjust the frequency by moving said crystal within the xed gap.

2. A piezo-electric crystal housing including an insulating housing, a plurality of electrodes within said housing, insulating members between said electrodes, forming an air gap, and a piezoelectric crystal interposed between lower and upper electrodes, and a plurality of adjusting means having ends tapered to a substantial point to hold said crystal in several different desired positions on the lower electrode and between said electrodes.

3. A piezo-electric crystal housing comprising an insulating cup-shaped housing, a plurality of electrodes spaced apart within said housing, to

:Us di forman air gap, a piezo-electric crystal interposed between said electrodes and adjustable finger-like elements having ends tapered to a substantial point adapted to retain different sizes of crystals iirmly in place within said air gap.

4. A piezo-electric crystal holder comprising a cup-shaped insulating housing, a lower electrode Within said housing, a plurality of insulating members secured to said lower electrode for spacing an upper electrode, a piezo-electric crystal interposed between said electrodes, a plurality of retaining means having ends tapered to a substantialrpoint for contacting the sides of said crystal to position said crystal in several diierent desired positions contiguous to said retaining means on the surfaceV of said lower electrode.

5. A piezo-electric crystal holder comprising a cup-shaped insulating housing, a lower electrode within said housing, a plurality of insulating members secured to said lower electrode and spaced substantially 120 degrees apart, for spacing an upper electrode, a piezo-electric crystal interposed between said electrodes, a plurality of retaining means having ends tapered to a substantial point for contacting the sides of said crystal to position said crystal in several different desired positions contiguous to said retaining means on the surface of said lower electrode.V

6. A piezo-electric crystal holder comprising a cup-shaped insulating housing, a lower electrode within said housing, a plurality of insulating members securedto said lower electrode for spacing an upper electrode, a piezo-electric crystal interposed between said electrodes, a plurality of retaining means having ends tapered to a substantial point for contacting the sides of said crystal to position said crystal in several different desired positions contiguous to said retaining means on the surface of said lower electrode, and a cover over the upper electrode, said cover secured in position by a concaved spring.

7. A piezo-electric crystal housing comprising an insulating cup-shaped housing, a plurality of electrodes, insulating members between upper and lower electrodes forming an air gap, a piezoelectric crystal interposed between said upper and lower electrodes, a plurality of eccentric positioning and retaining means to maintain the frequency of oscillations constant by holding said crystal in one of the severalY possible positions contiguous to said retaining means on the lower electrode within the air gap.

8. A piezo-electric crystal housing comprising an insulating housing, a plurality of electrodes, insulating members between upper and lower electrodes forming an air gap, a piezo-electric crystal interposed between said upper and lower electrodes, a plurality of movable metallic eccentrically shaped retaining members mounted around said crystal to maintain the frequency of terposed between said upper and lower electrodes', 45

a plurality of tapered retaining fingers to retain the frequency of oscillations constant by holding said crystal on the lower electrode within the air gap in one of several possible positions contiguous to said retaining fingers.

RALPH E. FRANKLIN. 

